The prior art has recognized the importance of preparing food products having high quality protein and has suggested a number of specific procedures for achieving this goal. For example, in U.S. Pat. No. 2,344,229 to Block et al., it is disclosed that animal foods prepared especially for chickens and dairy cows can be fortified with essential amino acids to reduce the required percentage of protein in the product. In addition to the usual listing of amino acids, it is indicated that glycine, usually considered a non-essential amino acids, can be required by some animals under certain conditions, especially as a detoxicating agent or to promote growth of chicks. Also along this line, Cornelius et al. in U.S. Pat. No. 4,024,286, disclose the fortification of foodstuffs by the addition of a bland methionine dipeptide containing glycine, alanine, valine, or glutamic acid as the second amino acid.
Other patents have suggested adding specific amino acids or reaction mixtures of these as flavoring materials. Specifically, U.S. Pat. No. 3,524,747 to O'Hara et al. teaches the preparation of a seasoning composition containing amino acids, organic acids, nucleotides, and reducing sugars which is said to have a meat-like flavor after heating. Glycine is listed among other non-essential amino acids as being possible ingredients in this reaction mixture. It is also noted that other prior art indicates that glycine can be employed as a sweetener in certain food products. Also, in U.S. Pat. No. 3,922,365 to Ney et al., a mixture of at least three amino acids, with glycine as an optional component, is said to impart a ripe cheese-like flavor to foodstuffs.
Yet other patents have suggested the use of non-essential amino acids including glycine in various connections with color retention in proteinaceous food products; however, none of these references relate to the stabilization of protein quality against the adverse effect of the Maillard reaction or processing conditions. For example, in U.S. Pat. No. 3,552,978 to Inklaar, it is disclosed that certain amino acids or salts which have a buffering capacity in aqueous solution can be employed to improve qualities of moisture retention, color retention, texture and taste. The disclosure of U.S. Pat. No. 3,617,307 is a continuation-in-part of that Inklaar patent and identifies the further advantage that such additives enable the use of extra protein without the formation of deleterious jelly and fat deposits. Also relating to color stabilization is U.S. Pat. No. 3,911,146 to Hara et al. which discloses that the color of meat can be preserved by contacting it with water-soluble ingredients of edible vegetal matter and that this effect can be enhanced by the addition of amino acids. Thus, while relating broadly to color retention, none of the patents teach or suggest the use of glycine to stabilize the protein quality of a food product containing protein and reducing sugars.